Linear polyesters such as poly(alkylene terephthalate) are generally known and commercially available where the alkylene typically has 2 to 8 carbon atoms. Linear polyesters have many valuable characteristics including strength, toughness, high gloss, and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a dicarboxylic acid or its functional derivative, typically a diacid halide or ester. Linear polyesters may be fabricated into articles of manufacture by a number of known techniques including extrusion, compression molding, and injection molding.
Recently, macrocyclic oligoesters were developed that have unique properties that make them attractive for a variety of applications, including as matrices for engineering thermoplastic composites. Macrocyclic oligoesters exhibit low melt viscosity, for example, allowing them easily to impregnate a dense fibrous preform followed by polymerization to polymers. Furthermore, certain macrocyclic oligoesters melt and polymerize at temperatures well below the melting point of the resulting polymer. Upon melting and in the presence of an appropriate catalyst, polymerization and crystallization can occur virtually isothermally.
Production of macrocyclic oligoesters such as macrocyclic (1,4-butylene terephthalate) typically involves the use of one or more solvents such as o-dichlorobenzene or xylene. Some prior techniques that have been used to recover macrocyclic oligoesters dissolved in a solvent required the addition of a large amount of anti-solvent to the solution to precipitate the macrocyclic oligoester followed by collection of the product using a filter or a centrifuge. The use of anti-solvents results in increased processing complexity, costs, and creates additional environmental storage and disposal concerns.
Linear polyesters may be depolymerized to form macrocyclic oligoesters. The product solution of a depolymerization reaction may be dilute, making recovery more time consuming. Depolymerization production efforts also generally take place in stages, with each stage including a step of the process and with intermediate storage between the steps.